I am in the UK as well (not that it matters other than hey - isn't this snow cool!) and I started off with a Kindle 6, loved the fact I could get my RSS feeds (via calibre->free.kindle.com) to magically appear on my device each morning.
Then I started a Masters, realised I needed a larger screen for the PDFs and purchased the Kindle DX - at quite a lot of money what with our poor exchange rate. Fell in love with that, but don't make the same mistake I made of thinking it was basically a bigger version of the 6". The firmware is very different (i.e. crappy web browser) and there is no wifi so no more freebie delivery of RSS feeds and the keyboard is *horrible* for typing on.
Eventually I caved in and purchased the iPad. I am a Software Engineer and spend 10+hours a day looking at a computer, hence my reluctance at purchasing an iPad, but I have to say I haven't regretted it for a second - it fits my needs perfectly.
HOWEVER!!! Trying to read the iPad anywhere near a strong natural light source (i.e. even indoors with your back to a window) is going to make you weep. Having said that, reading at night is much nicer on the iPad then the Kindle.
So - if you want a light weight reading device that you can toss in a back and read anywhere you like - the kindle is unbeatable. If you want a very powerful document reader (editor/annotator/free hand note taker) then the iPad is without doubt the right tool for the job.
I obviously returned both kindles, but sometimes I wish I hadn't returned the 6" when casually reading
